Project Summary. Excessive alcohol use is among the leading causes of preventable death worldwide and costs the USA over $223 billion a year. Stress and nicotine (from tobacco) are well-known risk factors for heavy alcohol consumption and alcohol use disorders. Despite the consistent human epidemiological evidence, in experimental models stress does not always produce increased alcohol consumption. The controversy arises, in part, because the neural mechanisms underlying the interactions among stress, nicotine, and alcohol remain significantly unknown. This proposal arose from our preliminary results showing that pre-exposure to acute nicotine or stress under strictly defined experimental conditions increases alcohol self-administration. We showed in rats that nicotine (like stress) boosts corticosterone levels in rats. Nicotine- or stress-induced glucocorticoid receptor activity is necessary for the subsequent increase in alcohol self-administration that arises owing to altered midbrain GABAergic circuitry. When we inhibited the nicotine/stress-induced glucocorticoid signaling or corrected midbrain GABAergic dysfunction, then alcohol self-administration returned to control levels. In the proposed studies, we will move from the simple acute exposures to nicotine and stress to more biologically realistic experimental situations. Lifetime nicotine and tobacco use almost always begins during adolescence, and adolescent smoking and childhood maltreatment are both high risk factors for increased alcohol consumption and alcohol use disorders in adulthood. Therefore, we will expose adolescent rats to nicotine or stress then allow the animals to age before analyzing their alcohol drinking behavior compared to control rats. Our preliminary results with adolescent nicotine treatments show that later in life, the adolescent- treated rats do drink more alcohol. Furthermore, the increased drinking requires glucocorticoid activity and arises from changes in midbrain GABAergic circuitry. We will measure the consequences of adolescent stress or nicotine exposure in adult rats during initiation, maintenance, extinction, and re-instatement of alcohol self- administration. The experiments will go on to investigate general circuit mechanisms underlying the increase in alcohol self-administration induced by adolescent nicotine or stress. Initially, we will be guided by our recent results indicating that a single, acute exposure to nicotine or stress induces an increase in alcohol self-administration by altering midbrain GABAergic circuitry. Then, guided by our preliminary results we will prevent or reverse the increased drinking caused by adolescent stress or nicotine via molecular and pharmacological manipulations within the midbrain. An aim is to identify a target and test a potential therapeutic drug to aid against increased alcohol consumption.